So from what I gather the mainsail is flattened at the leading edge in the area of the mast bend and then the leech would not have as much tension thus adding more twist and spilling more wind. It has been what I thought but have heard conflicting information.

I understand moving the top of the forestay aft and down would also decrease the tension on the leech of the headsail and so induce twist. Not sure about flattening the headsail though. If the foreatay tension is tight and is moved aft through increased backstay tension wouldn't this just decrease the angle of the straight line of the forestay and not reall effect the luff. But I guess it would all depend on the initial forestay tension.

As a broad general rule, as the wind increases the headstay sags more, and this is especially true on a fractional rig where the increased headstay forces induce more mast bend. When you tighten the backstay, this increases the tension on the forestay and that reduces this sag. When you reduce sag, almost by definition, the stay itself moves forward and to windward. And this increases the distance between the leech of the sail and the stay. As that distance increases, the jib is flattened and therefore depowered.

__________________To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay

Great explanation Jeff .thank you. ? Do you see any advantages to mast head rigs? Just came in from sailing. Variable day. Have Solent rig. Find if I leave tension on furled genny halyard a little loose get more out of the back stay.? Am I just fooling myself ? Obviously leave tension in actual stay the same all year once tuned.

Just want to point out how lucky we all are. We all have whatever level of experience, interest, academic background to opine on various topics. But we get to read and interact with a truly accomplished yatch architect.

It reminds me of a conversation I had years ago with a large animal vet (my wife is an equestrian and has had several horses over the years). He was describing his "experience" of horse owners.

"There are two ways I know of to becoming an equestrian vet and an expert on horses. The first is to go to college, go to veterinarian school, intern, pass your boards. The other is to buy a horse."

As a broad general rule, as the wind increases the headstay sags more, and this is especially true on a fractional rig where the increased headstay forces induce more mast bend. When you tighten the backstay, this increases the tension on the forestay and that reduces this sag. When you reduce sag, almost by definition, the stay itself moves forward and to windward. And this increases the distance between the leech of the sail and the stay. As that distance increases, the jib is flattened and therefore depowered.

Jeff

This explains the small triangle the Oday used to use on their rigs on the backstay. With the Mainsheet hooked to it, the more tension on the sheet, the tighter it pulled the stay

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